1. Field of the Invention
The present invention relates to liquid-level indicating windows.
A liquid-level indicating window for checking the liquid level is provided on a liquid container made of completely opaque material such as a metal or one made of an opaque or translucent synthetic resin, e.g., a reservoir tank for a car. For the brake fluid to be replenished properly, it is necessary that the lowering of the liquid level inside the reservoir tank or the current position of the liquid surface should be known exactly, simply through visual inspection.
2. Description of the Prior Art
The technical requirements imposed on liquid-level indicating windows include no liquid leakage at any time; easy attachment on the liquid container; sufficient resistance against vibration or shock; easy check of the window even while running; and no functional damage caused by mischiefs played while parking. In addition, the structure should be such that no breakage should be caused by high impact due to the occurrence of an accident. The liquid-level indicating windows of the prior art has had to be of a large size since the inside of the reservoir tank is usually dark or the reservoir tank is provided with a complete light-screening cover. With liquid-level indicating windows of large size, however, the light refraction at the surface of the liquid-level indicating window causes the lower level of the liquid to be observed only with great difficulty. Moreover, the reservoir for the master cylinder is usually too small to be equipped with a large-sized window. It is possible to substitute two liquid-level indicating windows of ordinary size for a large-sized window, but only with increased cost.